It is a wide-spread practice in the United States to provide railroad system railcar classification or marshalling yards with retarders that function to control the velocity of free-rolling railcars that are being classified and directed to various different tracks for routing to different destinations. Most such classification yards over the years have utilized retarder equipment falling into one of two basically different types.
Certain known train marshalling yards have utilized conventional mechanical retarders having movable metal surfaces, usually spring-urged, that press the faces of railcar wheel flanges passing through the retarders against the vertical faces of the adjacent supporting trackwork rails to create friction forces that reduce the railcar's free-rolling velocity. While such mechanical railcar retarders have substantial braking power and are of relatively simple design, their metal-to-metal braking contact is extremely noisy and causes substantial metal wear. Examples of such mechanical railcar retarders are disclosed in U.S. Pat. No. 1,452,556 issued in the name of Hackworth et al. and in U.S. Pat. No. 5,388,525 granted to Bodkin.
Other known railcar classification or marshalling yards have utilized conventional hydraulic retarders that basically utilize the weight of passing-through railcars to induce a hydraulic fluid damping that functions to reduce railcar rolling velocity. Typically the rim of a wheel flange engages the hydraulic actuator. Such hydraulic retarders have minimal metal-to-metal sliding friction surfaces thereby resulting in a significant reduction or equipment operating noise and also a significantly reduced extent of metal surface wear. However, such prior art hydraulic railcar retarders have substantial disadvantages in that the amount of railcar rolling energy that can be absorbed by their weight-induced fluid damping is comparatively limited, that there is a tendency for light-weight railcars to "jump" or "bounce" when rolling over the conventional retarder weight-actuated hydraulics element preset for heavier railcars and hence not be appreciably retarded, and also that there is an inability to control braking forces to achieve a predetermined and variable railcar retarded rolling velocity. In addition, current designs operate at a singular point, thereby concentrating their action within a very short and abrupt time period, further contributing toward the tendency for railcars to jump when rolling over the retarder.
We have discovered that the shortcomings of both known types of railcar retarder equipment can be overcome by utilizing a novel hydraulic railcar retarder assembly that is not activated by railcar weight but yet effectively reduces the momentum of railcars passing therethrough. This invention utilizes the railcar's momentum to activate the hydraulic railcar retarder. It also operates over a distributed area, thereby reducing the abruptness of braking forces so as to reduce the tendency of railcars to jump out of the retarder.
Other objects and advantages of the present invention will become apparent during consideration of the detailed descriptions, drawings, and claims which follow.